As the circuitry deposited on semiconductor chips has become even smaller, automated handling and precise positioning have become more and more important. The reduction in the size of the circuit elements has come to be limited by the wavelength of the light used to expose the photo resist. This problem has been met by employing light in the ultraviolet, and even in the X-ray regions of the spectrum. Considering the smallness of the circuit elements and the need for precisely overlaying each circuit over previous ones, the importance of each positioning of the wafer will be obvious.
It will also be obvious that dust and other foreign matter must be kept away from the wafer during processing. This practically necessitates the use of automatic handling equipment which may be housed in a closely controlled environment.